Persistent, loud noise in the workplace more than doubles the risk for heart disease, Canadian researchers say. Among those at highest risk are younger men who smoke, which by itself is a risk factor for heart disease, the study authors noted.

"Excess noise exposure in the workplace is an important occupational health issue, especially for younger workers," said lead researcher Dr Wen Qi Gan, from the School of Environmental Health at the University of British Columbia in Vancouver.

Persistent loud noise does not mean loud music or talking, Gan added, but rather any unwanted sound. In this study, noise was defined as industrial noise, such as noise in mining, lumbering and wood product manufacturing, Gan said.

"Noise control is critical to prevent these noise-related diseases. Whenever possible, protect yourself from exposure to excess noise," he advised. The report is published in the journal Occupational and Environmental Medicine.

The study

For the study, Gan's group collected data on 6,307 people aged 20 and older who took part in the US National Health and Nutrition Examination Survey between 1999 and 2004.

The participants were asked about their lifestyle and occupational health and other health-related topics, and underwent physical exams and blood tests.

The researchers divided the workers by the type of workplace they had: those who said they put up with persistent loud noise (making it difficult to talk at a normal level) for at least three months, and those whose workplace was relatively quiet.

Gan's team found that 21% of the individuals said their workplace was noisy almost all the time over a nine-month period. Most of them were men with an average age of 40. Compared with those who worked in a quiet environment, this group tended to be overweight and to smoke, which are risk factors on their own for heart disease.

The findings

But even after taking those risk factors and others into account, workers bombarded by a noisy environment were two to three times more likely to have serious heart problems than their counterparts in quiet workplaces, the researchers found.

The association between a noisy work environment and heart disease was particularly strong in those under 50 years of age, who were three to four times more likely to have angina or coronary artery disease or to have had a heart attack, Gan's team noted. Men and smokers in this age group were also at higher risk.

Blood tests of these at-risk workers did not show particularly high levels of cholesterol or inflammatory proteins, both of which are linked to heart disease. However, diastolic blood pressure - the second number in a blood pressure reading - was higher than normal, a condition linked to serious heart problems, the researchers pointed out.

In fact, those exposed to loud noise at work were twice as likely to have a higher-than-normal diastolic blood pressure, a phenomenon known as isolated diastolic hypertension, the researchers found.

The study was limited in that heart disease was based on self-reports of a doctor's diagnosis. Also, the research did not take into account other occupational factors associated with cardiovascular disease, such as shift work and air pollution, Gan's team noted, adding that more studies on the issue are needed.

Noise and emotion

The authors speculated that stress caused by loud noise could resemble that sparked by sudden, strong emotion, which over time can lead chemical messengers to constrict blood flow through the coronary arteries.

Dr William W. O'Neill, executive dean for clinical affairs at the University of Miami Miller School of Medicine and an interventional cardiologist, said with epidemiological studies, one cannot be certain of a cause-and-effect relationship - in this case, between a noisy workplace and heart disease.

But "intuitively it makes sense," he said. "It fits with the idea that stress is bad for your cardiovascular health."

Although the connection between noise and heart disease has not been proven, working in unpleasant conditions and the stress it produces can be bad for your heart, O'Neill said.

"If your work environment is really unpleasant, then in the long-term it's really bad for your cardiovascular system," he said.

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